Chromatography involves physically separating constituents of a sample in a carrier fluid and measuring the separation. In gas chromatography (GC) the carrier is a gas or at least a supercritical fluid which acts similarly in the system. In liquid chromatography (LC) the carrier is a liquid. In either case a pulse of the sample is injected into a steady flow of the carrier, and the constituents are adsorbed or absorbed and desorbed by a stationary phase material in a column. At the end of the column the individual components are more or less separated in time. Monitoring the column effluent with a suitable detector provides a pattern of retention times which, by calibration or comparison with known samples, indicates the constituents of the sample qualitatively and quantitatively. The main components of such a system are the column, an injector with a mixing chamber for introducing the sample into the carrier, a detector at the outlet end of the column, fluid controls, and a computer for processing and displaying the output of the detector. The display is generally in the form of retention times. In GC an oven generally is used to elevate temperature to maintain the sample in a volatile state, and to improve the discrimination of constituents. Various gas chromatographic systems are disclosed in U.S. Pat. Nos. 5,405,432, 5,545,252 ("Hinshaw 1"), U.S. patent application Ser. No. 08/734,689 filed Oct. 21, 1996 ("Hinshaw 2"), and an article "The Effects of Inlet Liner Configuration and Septum Purge Flow Rate on Discrimination in Splitless Injection" by J. V. Hinshaw, J. High Resolution Chromatography 16, 247-253 (Apr. 1993). A liquid chromatographic system is disclosed in U.S. Pat. No. 4,579,663.
Interpretations of retention time patterns in chromatography tend to require skill and experience, as different systems and particularly different columns behave differently so as to effect different patterns for the same sample material. An operator selects operating parameters, such as temperature and pressure, or may vary these parameters during a run, according to judgment. Thus uses of these systems for evaluating samples is dependent on the skills of the operators, and it has been difficult to compare results of different systems, columns and operators.
When a chromatographic method is developed it is often desirable to transfer it to the same system at a later time, the same system with a different column, or another system. The task is made more complicated by other factors including different calibrations of temperatures and pressures, and different oven geometries resulting in different temperature gradients. Differing characteristics of columns include length, internal diameter, phase thickness and phase chemistry, and these characteristics are difficult to determine with precision without destroying the column. These variations in systems, particularly columns, cause the retention times to change for different systems and the same system at different times, even switching the order of some peaks. Recalibration is complex and can be time consuming. Standardization would be desirable, such as is done in optical spectroscopy, for example as disclosed in U.S. Pat. No. 5,303,165 (Ganz et al.) It would be particularly desirable to be able to provide a useful library of basic standards associated with specified types of columns, so that chromatographic results may be compared universally.
Objects of the invention are to provide a novel method and a novel means for standardizing chromatographic systems so as to allow direct comparison of information generated from different systems and the same system at different times, including different chromatographic columns and the same column at different times. Particular objects are to provide a novel method and a novel means for establishing certain operating parameters for each chromatographic system such that retention times are substantially identical for different systems and the same system at different times. Other objects are to provide a novel method and a novel means for optimizing parameters for chromatographic systems. Additional objects are to provide a novel method and a novel means for measuring temperature of chromatographic columns, particularly to further standardization, and also to provide a novel method and a novel means for validating chromatographic systems.